BookGrabbr

A link might be helpful.

Never heard of it before, so I checked it out. My initial impression is that it's an interesting concept. However, without monetization, it will probably be one of hundreds of similar sites that fail after they run out of cash.

It's new to me, too. Does anybody have thoughts on what its advantages would be as compared to Rafflecopter?

It looks quite obscure to me, unlike other promotional services. In the Google app store they only have a couple of thousand downloads. I haven't seen any books promoted through that way on the social media I use. Although they claim that if an author shares the book to 50 people, that will lead to the book being eventually seen by 12500 people on social media. Their FAQ mentions them having 400 authors. And still I haven't seen any through my social feeds which are filled with people who read a lot.